Professor Shinji Toda, an expert on active faults in IRIDeS, calculated stress changes (changes in deformation before and after earthquakes) in the surrounding regions and faults after the magnitude 6.5 and 7.3 earthquakes, to find out the mechanism behind aftershocks which have been striking a wide area since April 16. In the figures below, stress is increasing in areas that are marked red, meaning fault activity may be induced, while regions marked in blue are places where stress is decreasing, thus fault activity seems to be on a downward trend (declining).

As a result, Professor Toda has concluded it is not the case that an unusual situation is occurring consecutively; the mechanism can be sufficiently and rationally explicable in today’s science, therefore, we should take the situation calmly, and carefully watch the development. He stated the following:

“Seismic activity which was activated along the Beppu – Yufu area and the northeast of Mount Aso (circled in green in the maps below) after the magnitude 7.3 earthquake, seems to have occurred because the balance of force in the surrounding region rapidly broke down, due to activity along the Futagawa fault which was the seismic center.

Although it is difficult to say when wide-spread aftershocks of the Kumamoto Earthquake will cease, there is no need to be terrified that an unprecedented natural disaster is happening. Aftershocks can be mostly explained by scientific knowledge, thus it cannot be said that an unusual situation is occurring consecutively. On the other hand, there is still strain unreleased on the Hinagu fault, where there is a series of faults continuing from the hypocentral region of the magnitude 6.5 and 7.3 earthquakes to the south, meaning that a strong tremor may occur, and it is necessary to continue to carefully observe changes in the situation.”

It is also important to understand the probability of large seismic intensity near one’s residence, using tools such as figures mapping the estimated seismic intensity when the Hinagu fault moves (in Japanese), and the J-SHIS Japan Seismic Hazard Information Station.

The above explanation is according to an estimation utilizing a simple model and is temporary, therefore, a more detailed analysis is still to come; we will update the latest information.

For further information or questions, please contact IRIDeS Public Relations Office:

+81-22-752-2049 or koho-office*irides.tohoku.ac.jp

(Please replace * with @)